3GPP LTE (3rd Generation Partnership Project Long Term Evolution) is the upcoming standard of 4th generation radio access networks. A continuing major challenge for designers is to reduce the system power consumption of mobile terminals, also known as User Equipment (UE) in LTE terminology.
FIG. 1 illustrates a protocol stack of a UE according to LTE standard specifications in the terms of the OSI (Open Systems Interconnection) model of logical layers. As is known in the art, the Non-Access Stratum (NAS) layer protocol is responsible for signalling and traffic between UE and the network for control purposes such as network attach, authentication, setting up of bearers, and mobility management. The Radio Resource Control (RRC) protocol of layer 3 is responsible for control plane signalling between a UE and the network, i.e. such tasks as broadcast of system information; establishment, maintenance and release of RRC connection; establishment, configuration, maintenance and release of signalling and data radio bearers; security functions including key management; mobility functions such as control of UE cell selection/reselection; paging; UE measurement configuration, processing and reporting; handover; quality of service (QoS) management functions; UE measurement reporting and control of the reporting, but not exclusively. Layer 3 interfaces with layer 2 and also directly interfaces with layer 1. Layer 2 of the protocol stack comprises a Packet Data Control Protocol (PDCP) sub-layer which is responsible for (de-) compressing the headers of user plane IP packets, a Radio Link Control (RLC) sub-layer which is used to format and transport traffic, and a Medium Access Control (MAC) sub-layer which provides addressing and channel access control mechanisms. Layer 3 interfaces with layer 2 and layer 1. Layer 1, also known as physical (PHY) layer, translates logical communication requests into hardware-specific operations such as modulation, bit synchronization, multiplexing, equalization, forward error correction etc. It has to be noted in this context that the above logical layers are typically reflected in the hardware implementation for a single UE as separate systems-on-a-chip (SoCs) which might even be provided by different vendors.
The LTE standard specifies a measurement procedure for UEs. The network instructs a connected UE to measure the signal power and quality of available base stations. Measurement results have to be reported to the network. The retrieved information is used by the network mainly to decide about the point of time as well as about the target base station of handovers. For each connected UE the network configures the downlink carrier frequencies it has to perform measurements on. Furthermore, the network configures reporting criterions within a UE in order to instruct the UE to only report relevant measurement results. According to protocol standards the measurement procedure of the UE is divided into functional tasks and assigned to different functional layers. Layer 3 filtering and the evaluation of reporting criteria are part of the RRC layer, as specified in LTE standard specifications TS36.331 and illustrated in FIG. 1.
If implemented in the RRC layer as per definition of the standard, some inefficiency with respect to power consumption is system immanent. The main issue is that the PHY reports every measurement result to the Radio Resource Control (RRC) layer. The RRC layer has to process all these results, filter them and check them against several reporting criterions in order to decide if they have to be reported to the network or not. The majority of PHY measurement results do not trigger a report to the network; hence the RRC entity is active although nothing has to be reported to the network.
A general object of the invention is to improve the system power consumption of user equipment (UE) of a wireless communications system. A more particular object of the invention is to improve UE power consumption when performing measurements.